The present invention pertains to wireless local area networks (WLANs), and more particularly, to methods of supporting idle stations in WLANs and wireless distribution systems (DS) operating under IEEE 802.11 standards.
In wireless local area networks, such as networks using the 802.11 model, consist of stations (STA) which are associated with access points (APs), which are in turn connected to a distribution system (DS). It should be noted that the DS is an abstract concept, and is not restricted to a particular implementation or technology.
FIG. 1 shows a wireless DS connected to a wired network as known to the art. DS 100 connects to wired network 200 through portal 110. Access points, 112, 114, 116, 118 provide wireless access to stations 120, 122, 124. As is known to the art, when a station associates with an AP, the DS is notified of this event so that incoming packets destined for the station are routed to the proper AP for delivery.
When a station is associated with an AP, such as station 124 associated with AP 116, implicit information is exchanged in order to keep the association state alive at both ends. For example, a STA may indicate to the AP that it is either going into power-save state or out of it by either setting bits in regular messages it sends to the AP or by sending a NULL data frame (a data frame with no payload) with bits in the header indicating change of state. The AP may set specific bits in the TIM (traffic indication map) information element in its beacons informing stations in power-save state that there may be packets buffered for them at the AP. Even though no explicit keepalive messages are exchanged, there is an expectation that an active connection be maintained by the station at all times.
In draft submission, document IEEE 802.11-07/2169r0 to the IEEE P802.11 group titled “Traffic Filtering and Sleep mode” on wireless LANs (incorporated herein by reference), a set of protocols and messages for supporting traffic filtering and idle mode is proposed. While the draft defines messages and behavior, it does not specify implementation details. Under the proposal, a station associated with an AP may specify filter parameters indicating what traffic it wishes to accept. When the station goes into sleep mode, it is no longer associated with a particular AP. The station is paged when traffic passing the pre-established filter criteria is met. When the station wakes from the sleep state, it reassociates with an AP.